This invention relates to breakerless ignition systems for use with spark-ignited internal combustion engines and deals more particularly with the construction and method of manufacture of the ignition coil module for use with an inductive type system.
The ignition system of this invention is particularly adapted for use in conjunction with small single cylinder internal combustion engines of the type commonly used for powering lawnmowers, snowblowers and the like.
Because of the highly competitive nature of the small engine market it is significant in carrying out this invention that the coil module be of unitary construction with a minimum number of parts so as to reduce the manufacturing costs and simplify its construction.
The prior art patent to Piteo U.S. Pat. No. 3,484,677 granted on Dec. 16, 1969, discloses a breakerless magneto ignition system of the inductive type in which the ignition coil and a trigger coil are both disposed within a unitary housing mounted on one leg of a ferromagnetic core. The patent to Burson U.S. Pat. No. 4,037,201 dated July 19, 1977, discloses a unitary coil module composed of a unitary plastic housing also disposed on one leg of a laminated core. While in both of these prior patents assigned to the R. E. Phelon Company, also assignee of the present application, the coils of the ignition system are all disposed within the same housing, the coils are all disposed on the same core leg. As a result, the coil constructions shown in both of these prior patents do not lend themselves to an ignition system utilizing a separate trigger coil which is not part of the main flux carrying core of the ignition system.
Accordingly, it is the principal object of this invention to provide an improved coil module for an inductive ignition system of simple and economical construction in which a separate trigger coil and its core are disposed within the same housing as the ignition transformer coil, but are axially spaced from the ignition coil.
It is another object of this invention to provide a coil module of the above type in which the trigger core includes a shank portion and an asymmetrical pole piece disposed externally of the housing for improved performance.